Benzaldehyde dimethyl acetal, reaction with

Acetalization or ketalization with silylated glycols or 1,3-propanediols and the formation of thioketals by use of silylated 1,2-ethylenedithiols and silylated 2-mer-captoethylamines have already been discussed in Sections 5.1.1 and 5.1.5. For cyclizations of ketones such as cyclohexanone or of benzaldehyde dimethyl acetal 121 with co-silyl oxyallyltrimethylsilanes 640 to form unsaturated spiro ethers 642 and substituted tetrahydrofurans such as 647, see also Section 5.1.4. (cf. also the reaction of 654 to give 655 in Section 5.2) Likewise, Sila-Pummerer cyclizations have been discussed in Chapter 8 (Schemes 8.17-8.20). 

The second group of reactions is called vicinal difunctionalization. They embrace the C2 and C3 positions of the furan ring simultaneously. Thus, complex 3 (X = O, R = R = R = H) reacts with benzaldehyde dimethyl acetal to give 4H-furanium cation (the product of electrophile addition at C4), which experiences further attack by the methoxide group with formation of the acetal 8 (950M2861). This reaction is possible in the presence of the Lewis acid (BF3—OEt2). Reaction with methyl vinyl ketone in methanol, when run in identical conditions. 

A solution of TMSOTf 20 (3 pL, 0.017 mmol) in 1 mL acetonitrile is added at -20 °C under an argon atmosphere to a solution of benzaldehyde dimethyl acetal 121 (0.34 mmol, 51.7 mg) and (Z)-(5-trimethylsilyloxy-2-pentenyl)trimethylsilane 640 (94.9 mg, 0.412 mmol) in 3 mL acetonitrile. After 20 min at 20 °C the reaction is quenched with phosphate buffer (pH 7). The combined CH2CI2 extracts are washed with brine and dried (Na2S04) to give, after evaporation, 59.2 mg (99%) 647 [183] (Scheme 5.93). 

The product possesses a homoallylic stannane moiety, which can be utilized as a useful synthon for cyclopropane formation (Scheme 68). Upon treatment of the homoallylstannane with HI, destannative cyclization takes place to give cyclopropylmethylsilane.271,272 A Lewis acid-catalyzed reaction with benzaldehyde dimethyl acetal affords vinylcyclopropane.273... 

Reaction of 1 with benzaldehyde and zinc chloride gave a diastereomeric mixture (6) of R- and 5-2,3-O-benzylidene derivatives (4a and 4b). The former (4a) would be identical to the acetal described by Zinner et al. (3) as 2,4-O-benzylidene-D-ribono-1,5-lactone. This structure was further established as 4a, by chemical and physical studies of the product obtained on reaction of 1 with benzaldehyde dimethyl acetal (7). The 2,3-O-benzylidene derivative, obtained by Garegg et al. (8) on reaction of 1 with a,a-dichlorotoluene in pyridine, has the same properties as compound 4a, which would indicate the -configuration for the acetal carbon. 

Uranium(VI) fluoride in l,l,2-trichloro-l,2,2-trifluoroethane at 0°C oxidizes12 aldehydes to acid fluorides in moderate yields (e.g., heptanoyl fluoride from heptaldehyde in 47% yield, benzoyl fluoride from benzaldehyde in 40% yield) benzaldehyde gives methyl benzoate and benzaldehyde dimethyl acetal when the reaction mixture is worked up by quenching with methanol.13... 

Homo-Reformatsky reaction.1 The reaction of 1-ethoxy-1-trimethylsilyloxy-cyclopropane (1) with an aldehyde in the presence of ZnCl2 results in y-silyloxy esters via a zinc homoenolate (a) of ethyl propionate (equation I). Znl2 is the preferred catalyst in the case of reactions with acetophenone and benzaldehyde dimethyl acetal and in reactions of l-isopropoxy-l-(t-butyldimethylsilyl-oxy)cyclopropane with aromatic aldehydes. 

Propose a mechanism for the acid-catalyzed reaction of benzaldehyde with methanol to give benzaldehyde dimethyl acetal. 

TTie most common methods generally used to prepare benzylidene acetals involve (a) reaction of a diol with benzaldehyde in the presence of p-toluenesul-fonic acid or a Lewis acid (usually zinc chloride)144 145 — a reaction that is accelerated by ultrasonication146 — or (b) reaction of the diol with benzaldehyde dimethyl acetal (a,a-dimethoxytoluene) in the presence of camphorsuifonic acid or p-toluenesulfonic acid as shown in Scheme 3.79.147 Both 1,3-dioxolanes or 1,3-dioxanes can be formed under these conditions. Yields may be improved by running the reactions under reduced pressure to remove the methanol as it is formed.88-148... 

Commercially available Amberlite IR-120 (H -form) was used as an acid catalyst this resin is a divinylbenzene-crosslinked partially sulfonated gel-type polystyrene. As a base catalyst, PEG-PS resin-supported proline was employed. The reaction was performed in water-acetone-tetrahydrofuran (1 1 1 v/v/v) at room temperature in the presence of 20 mol. % of resin-supported proline and Amberlite. After 20 h, the reaction mixture contained the starting 4-nitro-benzaldehyde dimethyl acetal, 4-nitrobenzaldehyde and the corresponding aldol product with acetone in a ratio of 4 9 87. This means that both the... 

When either L-tartaric acid esters la,b or D-tartaric esters 2a,b are treated with benzaldehyde under acidic catalysis with Deair-Stark removal of generated water, good to excellent yields of either (4i ,5i )-(330) or (45, 5 S)-2-phenyl-l,3-dioxolane-4,5-dicarboxylates (331) are obtained [115,116]. Acetal exchange, which involves reaction of the tartaric diesters with benzaldehyde dimethyl acetal in the presence of an acid catalyst, is also an excellent protection method [117]. 

Lividomycin A is pentacyclic and is structurally more complex than lividomycin B however, die former was suitable for 1-N-acylation. Reaction of penta-ZV-(benzyloxycarbonyl) lividomycin A with benzaldehyde dimethyl acetal gave a tribenzylidene derivative which, on treatment with sodium hydride in N,W-dimethylformamide, gave the cyclic carbamate 214. Of importance was the fact that, although there are two pairs... 

A reinvestigation of the main product from reaction of D-ribono-lactone with benzaldehyde dimethyl acetal has shown that it is the 2,3-0-benzylidene derivative of the 1,4-lactone and not the 2,4- -benzylidene analogue of the 1,5-lactone as previously suggested. 

A tandem reaction using Ti +-mont and HT that comprises deprotection and aldol condensation from malononitrile and benzaldehyde dimethyl acetal as starting materials is outlined in Table 2. The product is obtained only when both Ti + mont and HT are present and it is synthesized by Ti +-mont-catalyzed deacetalization of benzaldehyde dimethyl acetal, followed by the aldol reaction of malononitrile with benzaldehyde. When either Ti +-mont or HT was replaced by a homogeneous reagent such as p-toluenesulfonic acid or piperidine, neither the deacetalization nor the aldol reactions occurred to any great extent. 

The intermolecular reaction of oxocarbenium ions with simple alkenes, less reactive carbon nucleophiles, is generally slow and inefficient. A recent paper has described that the (la)-promoted intermolecular reaction of acetals with vinylcyclopropane (22) gives 3,6-heptadienyl ethers (23) with high E selectivity [74]. The allylation mechanism involves the formation of a cyclopropylmethyl cation intermediate and its ring opening (Scheme 9.21). Homoallylstannane (24) also adds to the oxocarbenium ion generated from benzaldehyde dimethyl acetal and (la) [75]. 

The latter reaction could be repeated ten times without loss of activity of Yb-XN-1010. Similar results were obtained with ytterbium(III) loaded Amberlyst 15W resin in a two-step one-pot procedure first involving the formation of the active dimethyl acetal from a benzaldehyde derivative which was followed by in situ protection of sucrose (Scheme 4.17) [100]. 

In reaction with benzaldehyde or its dimethyl acetal, or benzylidene dibromide, sucrose undergoes conversion into its 4,6-acetal in moderate yield (28-35%).160,161 The transacetalation reaction of dialkyl acetals prepared from unsaturated or aromatic aldehydes can take place under very mild acidic conditions. For example, sucrose-derived monomers or surfactants (variously substituted 4,6-(9-methylidenesucroses) have been prepared146,162 and 4,6-monoacetals incorporating masked aromas or fragrances derived from p-citral or a- or p-ionone were prepared directly from sucrose in high yields.163,164 These latter molecules, whose unsaturated carbonyl system is very susceptible to oxidation, are thus temporarily protected and are readily released under very mild conditions (Scheme 13). 

The formation and intramolecular dipolar cycloaddition of azomethine ylides formed by carbenoid reaction with C=N bonds has recently been studied by the authors group.84 Treatment of 2-(diazoace-tyl)benzaldehyde O-methyl oxime (176) with rhodium(II) octanoate in the presence of dimethyl acetylenedicarboxylate or N-phenylmaleimide produced cycloadducts 178 and 179, respectively. The cycloaddition was also carried out using p-quinone as the dipolarophile. The major product isolated corresponded to cycloadduct 180. The subsequent reaction of this material with excess acetic anhydride in pyridine afforded diacetate 181 in 67% overall yield from 176. The latter compound incorporates the basic dibenzofa, d -cyclohepten-5,10-imine skeleton found in MK-801,85 which is a selective ligand for brain cyclidine (PCP) receptors that has attracted considerable attention as a potent anticonvulsive and neuro-protective agent.86,87... 

A powerful oxidizer. Explosive reaction with acetaldehyde, acetic acid + heat, acetic anhydride + heat, benzaldehyde, benzene, benzylthylaniUne, butyraldehyde, 1,3-dimethylhexahydropyrimidone, diethyl ether, ethylacetate, isopropylacetate, methyl dioxane, pelargonic acid, pentyl acetate, phosphoms + heat, propionaldehyde, and other organic materials or solvents. Forms a friction- and heat-sensitive explosive mixture with potassium hexacyanoferrate. Ignites on contact with alcohols, acetic anhydride + tetrahydronaphthalene, acetone, butanol, chromium(II) sulfide, cyclohexanol, dimethyl formamide, ethanol, ethylene glycol, methanol, 2-propanol, pyridine. Violent reaction with acetic anhydride + 3-methylphenol (above 75°C), acetylene, bromine pentafluoride, glycerol, hexamethylphosphoramide, peroxyformic acid, selenium, sodium amide. Incandescent reaction with alkali metals (e.g., sodium, potassium), ammonia, arsenic, butyric acid (above 100°C), chlorine trifluoride, hydrogen sulfide + heat, sodium + heat, and sulfur. Incompatible with N,N-dimethylformamide. 

In the presence of weaker bases than butyllithium or sodamide active methyl groups are still able to take part in a variety of condensation reactions with carbonyl compounds. In fact, only catalytic amounts of the proton acceptor may be needed. Thus, 2-methylimidazole reacts with benzaldehyde to form the 2-styryl compound ((187), and l,2-dimethyl-5-nitroimidazole condenses with dimethylformamide dicyclohexyl acetal to give an 86% yield... 

Dimethyl-6-nitroquinoxaline (3) undergoes reaction with benzaldehyde in acetic anhydride to yield 2,3-distyryl-6-nitroquinoxaline (4). ... 

TABLE VI. Extinction coefficient of some products of the photo Fries reaction of poly 4-vinyl phenyl benzoate). Poly VB Poly (4-vinyl benzaldehyde) obtained by treating the copolymer with its dimethyl acetal by acidic solution. 

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